2. Discussion of the Prior Art
There is an extensive body of patents that require extensive modification of the frame of the bicycle in order to assist the rider or to fully power the vehicle. The vast majority of these ingenious mechanisms are worthless if one is contemplating a modification of an existing machine. The modifications range from a radical redesign of the frame and transmission to a large and ungainly addition to the front or rear wheel. A few of the most notable innovations in the field of motorized bicycle drive systems include several systems driving the pedals, or cranks arms of the bicycle. The advantages of this approach are numerous, especially when taken in conjunction with a modern multi-speed bicycle.
“Pedelecs”, as these systems are known, take advantage of the derailleur transmission system used by the rider. By driving the pedals through a suitable reduction gearbox, a Pedelec uses the derailleur system to keep the electric motor at the optimum speed to either produce maximum power, or operate at maximum efficiency. Murphy (U.S. Pat. No. 5,242,028), for example, describes a system in which two freewheels are used in conjunction with a motor, gearbox, and modified chain wheel crank in order to realize this advantage. The system described by Murphy allows power to be supplied by the rider or the motor. Rizzeto describes a similar system described (EP 0968911a1) in which a motor drives a modified chain ring assembly through a system having two freewheels. Rizzeto describes a system that has similar advantages in that power contributed by the rider and motor are independent. Both systems, however, are unnecessarily complex and expensive. Both systems require two freewheels, or overrunning clutches, and both systems require replacement of the chain rings attached to the pedals of the bicycle. This requirement not only requires a significant monetary expenditure on the part of the aspiring motorist, but also raises the possibility that extensive adjustment and debugging will be required to get the system to function properly, since it is well known that bicycle derailleur systems must be tuned and adjusted extensively. Any disturbance or replacement of part of the bicycle transmission is therefore undesirable.
Rizzeto describes a pedal crank that “is subject to high precision machining,” and Murphy places a roller clutch at the critical core of his mechanism. Roller clutches are notoriously sensitive to the surface finish and cleanliness of the shaft against which they operate. Both Murphy and Rizzeto fail to mention how to accommodate the various control cable positions which are typically placed along the down tube of a bicycle having rear, and optionally, front derailleur or other gear change mechanisms. None of these liabilities are necessary. It is possible to greatly decrease the complexity and cost of the system while providing much of the benefit described by Murphy and Rizzeto.